There have been known image forming devices that include a belt conveying device and an image forming unit. The belt conveying device includes a conveyor belt for conveying a recording sheet mounted on a conveying surface thereof. The image forming unit is disposed opposing the transfer surface of the conveyor belt and forms an image on a surface of the recording sheet conveyed by the conveyor belt.
In such an image forming device, if air is trapped between the recording sheet and the conveying surface of the conveyor belt when the recording sheet is placed on the conveyor belt, the recording sheet is partially raised from the conveying surface in some cases. Such partial rising of the recording sheet adversely affects image forming operation performed by the image forming unit, causing deterioration in image quality.
In order to cope with this problem, U.S. Pat. No. 5,740,512 proposes an image forming device that has a pressing member disposed near the upstream side of a conveyor belt in a sheet conveying direction. The pressing member has a plane pressing surface whose width gradually becomes wider from the upstream side toward the downstream side in the sheet conveying direction, and a downstream end of the pressing member having the wider width always contacts the conveying surface of the conveyor belt. In this image forming device, a recording sheet conveyed to the belt conveying device is first pressed toward the conveying surface of the conveyor belt by an upstream section of the pressing surface having the narrow width, and then, gradually press-widened starting from the center in the width direction toward both widthwise ends by the pressing surface whose width grows wider toward the downstream side. As a result, air between the conveying surface of the conveyor belt and the recording sheet is pushed out to the both sides of the recording sheet. In this manner, image quality is prevented from being deteriorated due to air trapped between the conveying surface of the conveyor belt and the recording sheet.
In an image forming device, a printing test is typically performed in an initial operation time so as to confirm whether or not an adequate printing result can be obtained (e.g., whether printing position or image density is proper or not), and printing operation is adjusted based on the results of the printing test. This printing test is performed by printing a predetermined test pattern on the conveying surface of the conveyor belt and detecting the test pattern using a sensor.